SLVAFO8A April   2024  – May 2024 DRV8214 , DRV8234

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction: Need for Sensorless Designs
  5. 2Ripple Counting − Concept
    1. 2.1 Ripple Counting Algorithm Details
  6. 3Case Study: Robotic Wheel Drive
    1. 3.1 Robotic Wheel Motor Operating Conditions
    2. 3.2 Tuning Parameters for Ripple Counting
      1. 3.2.1 Resistance Parameters
      2. 3.2.2 KMC and KMC_SCALE
        1. 3.2.2.1 Tuning KMC_SCALE
        2. 3.2.2.2 Tuning KMC
    3. 3.3 Robotic Wheel Motor with Ripple Counting
      1. 3.3.1 Inrush and Steady State Performance
        1. 3.3.1.1 Motor Speed Calculation
      2. 3.3.2 Soft Start
      3. 3.3.3 Loaded Conditions
  7. 4Challenges and Workarounds
    1. 4.1 Low Average Currents
    2. 4.2 Motor Inertia During Stop
    3. 4.3 Inrush
    4. 4.4 High Load Conditions
  8. 5Summary
  9. 6References
  10. 7Revision History

3.3.3 Loaded Conditions

Steady-state current waveform for on-load conditions is shown in Figure 3-9. Full load (stall) current was observed to be 1.3A. Motor was loaded at 50% of the full load current value, for example, 650mA. PWM duty cycle is 100%.

Steady State Performance at 50% Load Figure 3-9 Steady State Performance at 50% Load

Counting is done for 5 revolutions at steady state. Calculation for accuracy is shown in Table 3-9.

Table 3-9 Accuracy at 50% Load
Parameter 50% Load
Encoder Counts 20
RC_OUT Counts 30
Accuracy 100%

Figure 3-10 displays the performance of ripple counting during transitory loading. Change in load occurs from 10% to 60% over approximately 80ms. Counting is performed for 6 revolutions of the motor.

Figure 3-11 displays the performance of ripple counting during unloading. Change in load occurs from 60% to 10% over approximately 80ms. Counting is performed for 6 revolutions of the motor.

Transient Loading Figure 3-10 Transient Loading
Transient Unloading Figure 3-11 Transient Unloading

Table 3-10 shows the calculation for accuracy during both conditions.

Table 3-10 Accuracy During Transient Conditions
Parameter Transient Loading Transient Unloading
Encoder Counts 24 24
RC_OUT Counts 36 36
Accuracy 100% 100%